Method and apparatus for scheduling wafer processing within a multiple chamber semiconductor wafer processing tool having a multiple blade robot

Abstract

Apparatus and concomitant method for performing priority-based scheduling of wafer processing within a multiple chamber semiconductor wafer processing system (cluster tool) having a dual blade wafer transfer mechanism. The sequencer assigns priority values to the chambers in a cluster tool, then moves wafers from chamber to chamber in accordance with the assigned priorities. The sequencer is capable of determining the amount of time available before a priority move is to be performed and, if time is sufficient, the sequencer performs a non-priority move while waiting. The sequencer also dynamically varies assigned priorities depending upon the availability of chambers in the tool. Lastly, the sequencer prioritizes the chambers based upon the minimum time required for the wafer transfer mechanism to move the wafers in a particular stage.

What is claimed is: 
     
       1. A method for transferring a plurality of semiconductor wafers for processing within a multiple chamber, semiconductor wafer processing system having a plurality of chambers that are serviced by at least one multiple blade wafer transfer mechanism, said method comprising: assigning a priority to each chamber, each wafer, or both in said plurality of chambers;   assigning to each chamber, each wafer, or both a priority index;   scanning each stage of a process trace for a chamber having a highest priority index and that contains a wafer;   selecting said chamber;   positioning a first blade of said multiple blade wafer transfer mechanism proximate the selected chamber;   retrieving the wafer from the selected chamber using said first blade;   determining if a target chamber for the wafer on said first blade is empty and, if the target chamber is empty, placing the wafer on said first blade in the target chamber; otherwise, positioning a second blade of said multiple blade wafer transfer mechanism proximate said target chamber and retrieving said wafer from said target chamber using said second blade, then placing the wafer on said first blade into said target chamber.   
     
     
       2. The method of claim 1 further comprising the steps of: determining a time to complete (T remains ) processing for the selected chamber;   computing a time to perform (T meanwhile ) a wafer move for at least one other chamber;   dividing T meanwhile  by T remains  to produce a quotient;   comparing the quotient to a threshold value;   if the quotient is less than the threshold value, then move the wafer in the selected chamber; and   if the quotient is greater than the threshold value, then move a wafer in the other chamber.   
     
     
       3. The method of claim 1 further comprising the step of dynamically assigning priority to each chamber. 
     
     
       4. The method of claim 1 wherein, if a wafer in said selected chamber is not completely processed, said transfer mechanism waits for said wafer to be completely processed. 
     
     
       5. The method of claim 1 wherein said target chamber is one of a plurality of target chambers and said target chamber is selected based upon the target chamber with the highest priority index. 
     
     
       6. A method for transferring a plurality of semiconductor wafers for processing within a multiple chamber, semiconductor wafer processing system having a plurality of chambers that are serviced by at least one multiple blade wafer transfer mechanism having at least two independently movable blades, said method comprising: assigning to each chamber, each wafer, or both a priority index;   identifying a source-target chamber pair having a highest priority index;   selecting said source-target chamber pair;   simultaneously positioning a first blade of said multiple blade wafer transfer mechanism proximate the source chamber and positioning a second blade of said multiple blade wafer transfer mechanism proximate the target chamber;   retrieving a wafer in said source chamber using said first blade whenever said wafer is ready for transfer;   retrieving a wafer in said target chamber using said second blade whenever said wafer is ready for transfer;   placing said wafer on said first blade into said target chamber;   determining if a target chamber for the wafer on said second blade is empty or a loadlock and, if the target chamber is empty or a loadlock, placing the wafer on said first blade in the target chamber for the wafer on the second blade; otherwise, positioning the first and second blades proximate said target chamber and retrieving said wafer from said target chamber using said first blade, then placing the wafer on said second blade into said target chamber.   
     
     
       7. The method of claim 6 further comprising the steps of: determining a time to complete (T remains ) processing for the source-target chamber pair;   computing a time to perform (T meanwhile ) a wafer move for at least one other source-target chamber pair;   dividing T meanwhile  by T remains  to produce a quotient;   comparing the quotient to a threshold value;   if the quotient is less than the threshold value, then move the wafer in the source-target chamber pair; and   if the quotient is greater than the threshold value, then move a wafer in the other source-target chamber pair.   
     
     
       8. The method of claim 6 further comprising the step of dynamically assigning priority to each chamber. 
     
     
       9. Apparatus for scheduling semiconductor wafers for processing within a multiple chamber, semiconductor wafer processing system, said apparatus comprising: a sequencer for assigning a priority to each chamber in said plurality of chambers, each wafer in said plurality of wafers, or both and for selecting a chamber or wafer having a highest priority; and   a wafer transfer robot, coupled to said sequencer, for moving a wafer from a selected chamber or wafer to a target chamber in accordance with the assigned priority of the selected chamber, said wafer transport robot having at least two blades for carrying wafers from chamber to chamber.   
     
     
       10. The apparatus of claim 9 wherein the sequencer further comprises: means for determining a time to complete (T remains ) processing for the selected chamber;   means for computing a time to perform (T meanwhile ) a wafer move for at least one other chamber;   means for dividing T meanwhile  by T remains  to produce a quotient;   means for comparing the quotient to a threshold value;   where, if the quotient is less than the threshold value, then the wafer transfer robot moves the wafer in the selected chamber; and   if the quotient is greater than the threshold value, then the wafer transfer robot moves a wafer in the other chamber.   
     
     
       11. The apparatus of claim 9 wherein the sequencer further comprises means for dynamically assigning priority to each chamber.